In order to observe an internal structure in a very small area of an object, a scanning transmission electron microscope (STEM), a transmission electron microscope (TEM), or the like is used. As a general observation method for observing the inside of the sample by using such an electron microscope, it has been known to place the sample, which is sliced thinly such that an electron beam can transmit therethrough, on a mesh sample base including a large number of holes, so as to obtain a transmission electron beam by a detector which is disposed opposite to an electron source side with respect to a sample surface. However, since the sample is configured to float over mesh holes in this method, an operation for mounting the sample on the sample base is extremely difficult. Therefore, in Patent Document 1, an electron detector which can be directly mounted with a sample for observation has been proposed.
Further, the very small area of the object can be observed not only by the electron microscope but also by an optical microscope. By using the optical microscope, it is possible to obtain color information which cannot be obtained in principle by the electron microscope. In the optical microscope, it is possible to obtain a transmitted optical image by irradiating a white light or a specific light from one surface side of the sample, and by imaging light having the color information emitted from the sample or absorbed in the sample by an optical system on the other surface side of the sample. Thus, for example, it is possible to stain only a specific area in a cell by adding a specific stain to a biological cell sample or the like, thereby observing which area is stained or not by observing the color. In particular, since the transmitted optical image has a higher resolution than that of a reflected optical image, it is widely used in fields of life science and pathological diagnosis.
While the color information cannot be obtained by the electron microscope, the electron microscope can observe with high resolution the very small area which cannot be observed by the optical microscope. Further, information obtained from an electron microscope image is information reflecting a density difference of the sample, and is different from information obtained by the optical microscope.